Wise use of inputs, agronomic practices pays off in economic yields for soybeans

Most of us are familiar with the expression, “I threw everything at it but the kitchen sink.” But you may not have heard it applied much in agriculture. Well, at least not until now.

That’s the name being given to a research project begun by the United Soybean Board in 2008. The project was designed to see what would happen if researchers threw “everything but the kitchen sink” at soybeans to see if they could economically increase production.

A study, developed by Palle Pederson when he was the Extension soybean specialist at Iowa State University, used an “omission treatment structure” to test the impact of multiple products on soybean yields.

The omission treatments included the entire Kitchen Sink treatment except one of the inputs. For example, to determine if fungicide seed treatments contributed to higher yields, some plots contained all of the high-input system products except fungicide seed treatments. Researchers then compared the yields. (The difference was 1.4 bushels or less per acre.)

Project managers point out that yield decreases when certain products or practices are omitted do not tell the whole story. (A 32-page report on the study has been compiled by Corn and Soybean Digest, a sister publication of Delta Farm Press and Southeast Farm Press. A website for the study is also under development.)

“When we applied all of these products, we did increase yield compared to the control,” says Wade Kent, a University of Minnesota researcher who worked on the study, which took place in Arkansas, Iowa, Kentucky, Louisiana, Michigan and Minnesota.

“They were increased by 4 bushels. If you start looking at what happens when we start removing one product, there was a slight decrease in yield. But you can’t say that just one product contributed to that yield response — it was a system, so there was likely some interaction. There are multiple things occurring in that system.”

All told, the three-year Kitchen Sink project involved 18 locations per year spread across the six states. As might be expected, the study provided a massive amount of data, according to Seth Naeve, Extension soybean specialist at the University of Minnesota who became the study’s principal investigator after Pederson left to join the private sector.

Smaller, regional studies can provide valuable information, but detailed observations of a wide variety of variables have yielded extremely high-resolution data. “The summary of this study is highly predictive of what’s going to happen on any field because we’ve looked at a wide range of environments,” says Naeve.

“The idea here is that multiple locations and historical responses are much more predictive of what’s going to happen on an individual farm than what happened on that farm the previous year.”

The biggest yield boost occurred when researchers switched from control plots planted on 30-inch rows to high input systems on narrow-row beans or soybeans planted on row spacings of 20 inches or less. The result: a gain of 6.9 bushels per acre across all locations.

But just changing row spacings without bringing in the rest of the high-input package did not make as much of a difference in yields. If you just went from 30- to 20-inch or less row spacings, the yield increase was an average of 2.9 bushels per acre. At today’s prices, that’s still upwards of $45 an acre in revenue but far less than $105 an acre for the full deal.

“When we applied all those products in the high-input system under wide-row spacing, we did increase yield significantly compared to its respective control,” says Minnesota’s Kent. “However, if a grower would switch from a wide-row spacing to a narrow-row spacing — not utilizing any products, just putting soybeans in a narrow-row spacing configuration — they can increase yield and have it comparable to a 30-inch system with all the inputs applied.”

Naeve says that’s the biggest take-home message of the study. “Of all the newfangled things we looked at, row spacing gave us the biggest yield increase. I think that’s really provocative for farmers.”

Chad Lee, Extension agronomist at the University of Kentucky, says narrow rows can be especially beneficial in soybeans double-cropped with wheat.

Wheat beans, as they are often called, typically are planted in dry soil conditions and are in a race to set and fill pods before fall arrives. Narrow rows allows plants to make greater use of sunlight and moisture.

In Arkansas, farmers may run the gamut from broadcast beans to 7.5-inch drilled beans to 38-inch planted rows. Though narrower-row spacings offer benefits of shading weeds and minimizing moisture loss, some growers are returning to wide rows because of the need to cultivate and remove glyphosate-resistant Palmer amaranth. If they can stay with narrow rows, that’s still the best approach, according to the study.

Another relatively low-cost input that provided some eye-opening results was seeding rates. Researcher Landon Ries at the University of Minnesota developed a protocol to compare seeding rates of 25,000, 75,000, 125,000, 175,000, 225,000 and 275,000 seed per acre in at least three locations per state.

In each one, researchers tested all the seeding rates on two varieties — one that was adapted to the area and a second variety that was one maturity group earlier. “We knew farmers were growing some earlier soybeans, and we’ve never given different recommendations based on maturity,” says Naeve.

Again, the breath of the Kitchen Sink project gave researchers access to a large amount of data spread over a wide array of environmental conditions and time. What they couldn’t help notice was how consistent the results were.

“I was really surprised that seeding rates in the South correspond with seeding rates in the North,” University of Arkansas Extension agronomist Jeremy Ross notes. “In the North, they have a shorter growing window, but about 175,000 seeds per acre was pretty much optimal from Louisiana up to Michigan.”

In general, the numbers indicate growers can increase yields with higher seeding rates, but Ries and his fellow researchers say they shouldn’t become fixed on a specific figure.

“The take-home point of this portion of the study is that there really isn’t an optimum seeding rate, but rather an optimum range, and that range is rather large,” says Ries. “If a farmer is shooting to be within 95 percent of maximum economic return, they could plant 120,000 seeds per acre and likely be fine.

“However, from our data, we see no economic disadvantage of planting what would be considered a rather high population, such as 190,000 seeds per acre. There is still a positive return up to that peak.”

In the study, Ries calculated an economic return based on a cost of $40 per 140,000-unit of seed and a $12-per-bushel average for the soybean price. Changing the cost of seed by $1 per unit only changed the economics of optimum population by about 300 seeds per acre. The relationship dropped by a corresponding amount when the soybean price decreased by $1 per bushel.

Shooting for 110,000 seeds per acre enabled researchers to achieve 95 percent of the maximum net return, while increasing the rate to about 150,000 seeds per acre took them to 99 percent of maximum net return. Planting 190,000 seed per acre put them at 100 percent. Beyond 190,000 seeds, the economic return curve began to drop.

“I used to tell farmers they would get a bushel back for every bushel more they plant,” says Naeve. “This new analysis seems to indicate farmers can anticipate well over a bushel of grain back by planting an extra half bushel (up to 190,000 seeds per acre). It appears that with high-priced grain right now, there is little downside risk with higher seeding rates.”

Kentucky’s Chad Lee has a different take. “You could say, ‘I want to go ahead and plant lower rates, plant less seed, handle less seed overall and still make enough money.’ Other growers, when you say, ‘95 percent return,’ they say, ‘I want 100 percent.’

“But that 95 percent most of the time is going to capture economic yield, while if you’re going for 100 percent, from an economic standpoint most of the time you are not going to get extra yield to make up for the extra cost of the seed.”

Beyond the agronomic issues, the Kitchen Sink researchers also looked at the impact of commercially available inputs that have a reputation for helping growers increase their yields:

Preplant fertilizer. The study found upping fertilizer rates beyond soil test or Extension field trial recommendations did not provide an economic return. Only two sites in the study responded positively to increased fertilizer rates and those both tested in the medium to low categories prior to fertilizer being applied.

“Historically, I think a lot of our fields are going to require some preplant fertilizer, especially potassium,” says the University of Arkansas’ Ross. “We’ve always seen good response to potassium. We didn’t see an increase with additional fertilizer, but it really helps to put on the recommended nutrients.”

Seed inoculant. In general, researchers saw little benefit from adding a seed inoculant unless the field had been out of soybeans for five or more years.

Seed treatments. Using an insecticide/fungicide seed treatment resulted in an average difference of about one bushel per acre. But Arkansas’ Ross isn’t ready to write off seed treatments, especially in less-than-optimal planting conditions in which diseases such as Pythiumand Rhizoctonia and insects like bean leaf beetles, three-cornered alfalfa hoppers and thrips can thrive.

“Just by themselves, those pests don’t cause much of a problem, but if you get a little bit of this and a little bit of that, it can add up later in the season,” he notes. “We recommend fungicide and insecticide treatments, especially if you’re planting early in the season and have cool, wet conditions or if you’re going late with double-crop beans.”

Foliar fungicide. The authors called this the “shining star” in intensively managed soybeans. “Adding everything but foliar fungicide didn’t significantly increase yield, but when you subtracted that one input out of the mix, you reduced yield significantly,” says Minnesota’s Naeve.

None of the plots in the study had threshold-level outbreaks of foliar disease, though low levels of some diseases were present in many locations. Nor was there definite proof on whether the fungicides controlled the low levels of pathogens or provided the plant health benefits manufacturers claim for strobilurin fungicides.

“This is about the first time we saw what appears to be a consistent yield increase due to a fungicide without disease being present,” says Kentucky’s Chad Lee.

“For the most part, our disease pressure was pretty low. The results didn’t appear to be because of disease control. Because we are putting other inputs in there, it does make you think maybe something’s happening in conjunction with other products, but we can’t tell you why.”

Early- vs. late-season inputs. The Kitchen Sink protocol also tested early-season vs. late-season input timing. For the early/late plots, the researchers split the high-input program into preplant products vs. postemergence applications, applying plots with only pre-emergence and only post programs.

That is, the early-season program included preplant fertilizer, seed inoculant and seed treatment, but no postemergence applications; the late-season program started with bare seed and included only foliar fertilizer and foliar fungicide.

“There are farmers who buy everything up front, put everything down and walk away,” says Naeve. “That’s early-season management. The other test was based on a hypothetical farmer who just plants plain seed and manages the crop in-season.

Both the early- and late-season programs yielded significantly less than the high-input/narrow-row plots, though at a difference of 1.5 bushels per acre, the late-season approach was relatively close to the full high-input result.

Tradition has it that the Midwest and South are totally different regions that require their own unique approaches to growing soybeans. The Kitchen Sink project has called that assumption into question.

The authors note that one of the key goals of the Kitchen Sink project was to develop recommendations for high-yielding soybean production in any state where soybeans are grown.

With all the differences in climate, varieties, pest pressure and cultural practices between North and South, researchers weren’t sure if there would be enough common ground to make national recommendations. By the end of the three-year study, the scientists believed that national recommendations would indeed be valid.

“The bottom line is we’re all dealing with the same situations,” says the University of Arkansas’ Ross. “The same things that work in the South also work in the Midwest.”

“I’d examine the treatment figures by state and the same trends were always there,” says Minnesota’s Naeve. “It was really amazing that we had the same kind of responses across such broad geographies.”

The project’s lead investigator says several lessons can be learned from the study. For example, growing higher yields to win contests is one thing, but maximizing profit per acre is most important. That’s why the project has an economic component.

The latter indicates every combination of inputs — and the control plots — was profitable when soybeans were priced at $10 to $12 per bushel. Soil fertility treatments dragged down the profit, but stayed positive at those prices.

When soybeans were priced at $8 only the control plots and the late-season management trials — which included the foliar fungicide but not the soil fertility, seed treatment or seed inoculant — posted a positive return.

“If you’re going to spend money, it looks like managing late-season inputs is likely to have a greater effect on yield,” says Minnesota’s Kent. “And if you’re going to spend all that money, make sure some of that money is spent on foliar fungicides.”